This invention relates to a composition for the production of expanded materials which are stiff and self-supporting. More particularly, this invention relates to a composition based on an unsaturated polyester resin, an isocyanate, and a filler material. Unsaturated polyester resins have been used in the prior art in the manufacture of products such as building sheets, automobile fenders, boats, and the like, and have been used together with aqueous metal silicates, such as sodium silicate, for the production of laminated products containing reinforcing fibers or a core of expanded metal lath (see U.S. Pat. No. 4,011,195).
Plastic materials have been formed from compositions containing hydroxyl-terminated linear polyesters, an isocyanate, an aqueous alkali metal silicate and fillers (see U.S. Pat. Nos. 4,042,536; 4,097,422; 4,142,030; 4,057,519). These plastic materials contain aqueous alkali metal silicates, preferably sodium or potassium silicate, which chemically react with other components, and are used for products which may have a low strength compared to their specific density. The plastic materials obtained by such compositions are generally used as insulating panels or foams for coating buildings owing to their good fire and heat resistance.
As it is well-known from the prior art in the matter of expanded materials, the synthetic compositions often used as basic materials are characterized by the presence of isocyanates associated with polyols, and such materials can be expanded up to 10 times their original volume. The expanded materials thus obtained with a density of not more than 100 kg/m.sup.2 have a mechanical strength which is inadequate for a technically satisfactory use as structural materials and they do not have physical properties conducive to the production from them of articles of a large size and having self-supporting properties. On the contrary, there are obtained, as a rule, expanded products of a small size, which tend to crumble and do not hold screws, so that they are virtually incapable of withstanding ordinary mechanical stresses.
It is to be noted, in particular, that the defect of brittleness, in addition to restricting the field of application of the expanded materials to that of sound-absorbing and/or self-extinguishing fillers, requires the use of expensive metal supporting members such as zinc or aluminum to ensure adequate supporting strength. This has undesirable results during the manufacturing operations including an increase in scrap produced.